The delivery of volatile materials, such as fragrances (e.g., air fresheners) may be achieved by means of a delivery apparatus that includes a reservoir containing volatile material. The deliver apparatus typically includes a vapor permeable membrane that covers or encloses the reservoir. Volatile material within the reservoir passes through the vapor permeable membrane and is released into the atmosphere (e.g., air) on the atmosphere side of the membrane. Vapor permeable membranes are typically fabricated from organic polymers and are porous.
The rate at which volatile material passes through the vapor permeable membrane is generally an important factor. For example, if the rate at which volatile material passes through the vapor permeable membrane is too low, properties associated with the volatile material, such as fragrance, will typically be undesirably low or imperceptible. If, for example, the rate at which volatile material passes through the vapor permeable membrane is too high, the reservoir of volatile material may be depleted too quickly, and properties associated with the volatile material, such as fragrance, may be undesirably high or in some instances overpowering.
It is generally desirable to minimize or prevent the formation of liquid volatile material on the atmosphere or exterior side of the vapor permeable membrane, from which the volatile material is released into the atmosphere (e.g., into the air). Liquid volatile material that forms on the exterior side of the vapor permeable membrane may collect (e.g., puddle) within and leak from the delivery apparatus resulting in, for example, staining of articles, such as clothing or furniture, that come into contact therewith. In addition, the formation of liquid volatile material on the exterior side of the vapor permeable membrane may result in uneven release of volatile material from the delivery device.
Upon exposure to an increase in ambient temperature, the rate at which volatile material passes through the vapor permeable membrane may increase to an undesirably high rate. For example, a delivery apparatus that is used within the passenger compartment of an automobile may be exposed to increases in ambient temperature. As such, minimizing the increase in the rate at which volatile material passes through the vapor permeable membrane, as a function of increasing ambient temperature is typically desirable.
It would be desirable to develop new microporous materials that possess controlled volatile material transfer properties. It would be further desirable that such newly developed microporous materials minimize the formation of liquid volatile material on the exterior side or surface thereof. In addition, the rate at which volatile material passes through such newly developed microporous materials undergoes a minimal increase with an increase in ambient temperature.